A roadside bomb blast has killed at least 13 people in southern Afghanistan.

Provincial officials say the blast hit a vehicle carrying Afghan civilians as it traveled on a dirt road in the Maiwand district of Kandahar province. They said traffic had been diverted from the main road following a separate explosion targeting foreign troops.

The blast comes two days after Afghans cast their ballots for president and members of local provincial councils. The Taliban had threatened to disrupt Saturday's vote, but the election took place amid relative peace after several high-profile attacks targeting politicians, journalists and security forces in previous weeks.

The U.S. Department of Defense Monday hailed the "historic" election during which millions voted under the protection of Afghan security personnel - showing "how far Afghan forces have come." A Pentagon spokesman said U.S. and NATO forces provided advisory, air and emergency medical support, but "those were largely un-utilized."

Afghan voters chose a successor to President Hamid Karzai, who could not run for a third term and has been in office since U.S.-led forces ousted the Taliban government in 2001. Officials have begun counting ballots and preliminary results are expected on April 24.

The Pentagon said Monday it will encourage any government leaders who emerge from the election to "quickly engage" with the United States and sign the already negotiated Bilateral Security Agreement. President Karzai has refused to sign the deal that would allow some American troops to remain in Afghanistan in a training and advisory role after 2014. Mr. Karzai's office has said he wants U.S. assurances that it will play a key role in peace talks with the Taliban and stop nighttime raids on Afghan homes.

Afghan election monitoring groups said Monday that this year's election was "less fraudulent" than the 2009 presidential vote, but are asking candidates who suspect vote tampering to report any issues to the Electoral Complaints Commission.